1. Field of the Invention
The present invention relates to a magnetic separation apparatus and a waste water treatment apparatus, and more particularly to a magnetic separation apparatus and a waste water treatment apparatus that separates suspended solid, oil, or heavy metal from waste water containing suspended solid, oil, or heavy metal and obtains treated water.
2. Description of the Related Art
As an apparatus that separates suspended solid, oil, or heavy metal from waste water containing suspended solid, oil, or heavy metal, a waste water treatment apparatus using a magnetic separation apparatus has been conventionally known. The waste water treatment apparatus adds magnetic powder to waste water when coagulating and treating suspended solid, oil, or heavy metal contained in waste water, separates a coagulated floc (hereinafter referred to as a magnetic floc) containing magnetic powder with a magnetic force of the magnetic separation apparatus, and thus obtains treated water.
FIG. 6 is a block diagram showing a configuration of a waste water treatment apparatus 100 disclosed in Japanese Patent Application Laid-Open No. 2009-112978.
With the waste water treatment apparatus 100, waste water is mixed with magnetic powder (for example, ferrosoferric oxide) and an inorganic coagulant (for example, ferric chloride, polyaluminum chloride) in a rapid agitation vessel 102, and then mixed with a high molecular coagulant in a slow agitation vessel 104. A magnetic floc generated in the rapid agitation vessel 102 and the slow agitation vessel 104 takes in suspended solid, oil, or heavy metal in the waste water, and thus waste water is purified. The magnetic floc is separated by a floc separation device 106 provided in a subsequent stage of the slow agitation vessel 104. The floc separation device 106 includes a magnetic separation apparatus 108 and a filter 110. The waste water from which the magnetic floc is separated is treated water. The magnetic floc that has not been separated by the magnetic separation apparatus 108 is separated and removed by the filter 110 in a subsequent stage, and returned to the magnetic separation apparatus 108 and separated.
However, the waste water treatment apparatus 100 in Japanese Patent Application Laid-Open No. 2009-112978 can obtain clean treated water by providing the magnetic separation apparatus 108 and the filter 110 in line, but in order to prevent the filter 110 from being clogged, the filter 110 needs continuous back washing that requires a large filtering area. Specifically, the waste water treatment apparatus 100 in Japanese Patent Application Laid-Open No. 2009-112978 has an advantage that the magnetic separation apparatus 108 is used instead of a settling basin to significantly reduce an installation area, but requires a large filter 110, which loses an advantage of the magnetic separation apparatus 108.
A structure of a disk-type magnetic separation apparatus 120 disclosed in Japanese Patent Application Laid-Open No. 2009-101339 is shown in FIGS. 7 and 8. FIG. 7 is a plan view of the magnetic separation apparatus 120, and FIG. 8 is a front view of the magnetic separation apparatus 120, and a perspective view illustrating a separation vessel 122 having a semicircular section.
In the separation vessel 122 of the magnetic separation apparatus 120, disks 124 and 126 having a magnetic force are placed at a predetermined interval. A shaft 128 is secured to centers of the disks 124 and 126, and the shaft 128 is connected to an unshown motor. The motor rotates the disks 124 and 126 counterclockwise in FIG. 8 via the shaft 128. Height positions of the disks 124 and 126 are set so that when waste water flows into the separation vessel 122, lower halves of the disks 124 and 126 are submerged in the waste water.
A waste water supply portion 130 is provided in a center of a bottom of the separation vessel 122. Thus, coagulated waste water flows from the supply portion 130 into the separation vessel 122 as an upward flow, and is divided into two directions with the supply portion 130 at the middle. While the waste water is flowing toward treated water discharge ports 132 and 134 provided on opposite sides in an upper portion of the separation vessel 122, a magnetic floc in the waste water adheres to the disks 124 and 126. The magnetic floc adhering to the disks 124 and 126 is scraped by a scraper 136 provided between the disks 124 and 126 during rotation of the disks 124 and 126. The scraped magnetic floc is scraped by a sludge scraper 138 provided along the scraper 136 and discharged to the outside of the magnetic separation apparatus 120.
In the magnetic separation apparatus 120, there is a region in which a water flow direction in the separation vessel 122 is opposite to a rotational direction of the disks 124 and 126 (left portion viewed from the shaft 128 in FIG. 8). In this region, a force to release the magnetic floc adhering to the disks 124 and 126 is significantly applied to the magnetic floc by a flow of the waste water, which may slightly reduce quality of treated water. Thus, the magnetic separation apparatus 120 in Japanese Patent Application Laid-Open No. 2009-101339 requires a filter in a subsequent stage of the treated water discharge port 134.
A magnetic separation apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-131479 has a structure in which a magnetic floc generated by a coagulation device is once filtered by a rotary filter, and the magnetic floc on a surface of the rotary filter is adsorbed by a drum separator (magnetic drum) and scraped by a scraper.
The separator includes a magnet rotor including a group of magnets and a drum rotor that constitutes a surface of the magnetic drum, and the magnet rotor and the drum rotor may be integrally or separately rotatable. When an outer diameter of the magnet rotor is substantially the same as an inner diameter of the drum rotor, sludge or a transfer blade is provided near a position where the scraper that scrapes the magnetic floc is in contact with the drum rotor to facilitate discharge of the magnetic floc.
In the conventional waste water treatment apparatuses using a magnetic force as in Japanese Patent Application Laid-Open Nos. 2009-112978 and 2009-101339, a large filter is required in a subsequent stage of a magnetic separation apparatus in order to obtain clean treated water, which loses an advantage of the magnetic separation apparatus that an installation area can be reduced.
In the invention in Japanese Patent Application Laid-Open No. 2005-131479, a large rotary filter that determines treated water quality performance needs to be provided, and there is a defect such as clogging depending on waste water quality. Thus, an apparatus can be supposed that has a configuration only including a separator with a rotary filter removed from the structure in Japanese Patent Application Laid-Open No. 2005-131479, and adsorbs and separates a magnetic floc.
However, with the configuration only including the separator, a shear force is generated due to a difference between a circumferential velocity by rotation of the separator and a flow velocity of the waste water. Thus, if an rpm of the separator is increased to increase the number of discharged magnetic flocs particularly when raw water having high concentration is treated, a large shear force is generated between the separator and the magnetic floc. Since the magnetic floc adsorbed by the separator is very fragile, the magnetic floc is divided into fine flocs when the shear force is generated, and magnetic separation performance is degraded. Also, a shear force due to a difference between the magnetic force and a fluid force degrades the magnetic separation performance.